Yol. 57.] CORALLIAX OF ST. IVES AXD ELSWORTH. 



6. On tlie CoEALLiAN" Rocks of Sx. Iyes (Huntingdonshire) and 

 Elsworth. By Charles Bertie Wedd, Esq., B.A., F.G.S. 

 (Read December 5th, 1900.) 



[Communicated by permission of the Director-General of 

 H.M. Geological Survey.] 



(Map on p. 74.) 



I. Introductory Remarks. 



Lately while mapping the Arapthill Clay, I have been able to trace 

 the Elsworth and St. Ives Rock for a considerable distance. I 

 propose to give here a sketch of its outcrop and some account of 

 exposures not previously noticed. The district here treated of is 

 contained in the 1-inch quarter-sheets of the Geological Survey, 

 Nos. 51 north-west & south-west (western part) and 52 north- 

 east & south-east (eastern part), and in the l^ew Series Alap 

 Sheet 187 (not yet published). 



Erora Prof. Seeley's papers ^ the following description of the 

 Elsworth Rock at Elsworth may be extracted: — 



Feet. 



Eock-bed, like that below , 1^- 



Brown-black clay, with Ostrea flabelloides (Marshi) ; this bed 



passes into sandstone 5 



Dark blue homogeneous limestone, with ironshot oolitic 

 grains, and iron -pyrites 3 to 7 



It is known to occur throughout the village of Elsworth, passing 

 southward under Ampthill Clay with three whitish-grey stone- 

 bands. 



Prof. Seeley (oj9. cit.) also recorded rock-beds of type similar to 

 the Elsworth Ptock from wells at Bourn (3 miles south-south-west 

 of Elsworth), Papworth Everard, and Conington ; but he considered 

 that the rock at the latter two places belonged to a lower horizon 

 than that of Elsworth. 



In a brickyard west of St. Ives a like rock has long been known 

 (the St. Ives Rock); in other brickyards north and north-east 

 of St. Ives beds of rock were noticed by Prof. Seeley as dipping 

 eastward, and these he was inclined to think were continuous with 

 the Rock west of the town. 



A collection of fossils in the Woodwardian Museum, agreeing 

 closely with the fauna of the Elsworth and St. Ives Rock, was 

 supposed to have come from Holywell, but the occurrence of the 

 limestone there was not definitely known. The late Thomas Roberts "^ 

 mentioned a brown rock, as occurring at the northern end of 

 Swavesey village, at a depth of some 20 feet. West of Bluutisham, 

 north-east of St. Ives, a rock similar to that of Elsworth was 



J Ann. Mag. Nat. Hist. ser. 3, vol. viii (1861) p. 503 & vol. x (1862) p. 98. 

 - ' The Jurassic Rocks of the Neighbourhood of Cambridge ' (Sedgwick 

 Prize Essay for 1886) publ. 1892, p. 23. 



